Plastisol compositions obtained by dispersing polymer fine particles in a plasticizer, known as paste resins, are currently in wide used in industry for numerous uses such as coatings for automobiles, flooring materials, wallpaper, steel sheets and the like or as molding materials for slush molding, dip molding and rotation molding, and the most commonly used are vinyl chloride sols employing vinyl chloride resins as the polymer fine particles.
However, vinyl chloride resins are associated with the problem of production of the toxic substance dioxin when incinerated at low temperatures. In order to avoid this problem, acrylic sols, using acrylic-based resins as the polymer fine particles, have been proposed as substitute plastisol compositions in place of vinyl chloride sols.
For example, Japanese Unexamined Patent Publication No. 7-233299 discloses polymer fine particles, used in an acrylic sol composition, which are particles having a core/shell structure with a plasticizer-compatible core section and a plasticizer-incompatible shell section. These have been proposed because particles having such a structure offer improved storage stability in a sol state, and when the sol composition is coated and heated to form a gelled film, the morphology of the polymer fine particles is altered in such a manner as to improve mechanical properties of molded products obtained after heating.
In recent years, however, the specifications for the mechanical properties of molded products obtained using plastisol compositions have become even more demanding.
Japanese Unexamined Patent Publication No. 9-77950 proposes an acrylic sol comprising polymer particles composed of a copolymer consisting of a hydroxyl group-containing methacrylate and a different copolymerizable monomer, but it has not yet been possible to achieve coatings with sufficient mechanical properties even using this acrylic sol.
Thus, although acrylic sols using polymer fine particles with various structures have been proposed, it is still the case that non-vinyl chloride based plastisol compositions with very excellent mechanical properties, and which can substitute for vinyl chloride sols, have not yet been obtained.